This invention relates to the beneficiating or concentrating of ores. In particular, this invention relates to collectors useful in ore beneficiating.
Flotation is a process for concentrating minerals from their ores. Flotation processes are well known in the art and are probably the most widely used method for recovering and concentrating minerals from ores. In a flotation process, the ore is typically crushed and wet ground to obtain a pulp. Additives such as flotation or collecting agents and frothing agents are added to the pulp to assist in subsequent flotation steps in separating valuable minerals from the undesired, or gangue, portion of the ore. The flotation or collecting agents can comprise liquids such as oil, other organic compounds, or aqueous solutions. Flotation is accomplished by aerating the pulp to produce froth at the surface. Minerals, which adhere to the bubbles or froth, are skimmed or other removed and the mineral-bearing froth is collected and further processed to obtain the desired minerals.
The basic techniques behind froth flotation is to use chemicals to increase the hydrophobicity of the mineral to be beneficiated to form a concentrate. Meanwhile, chemicals are added, as necessary, to decrease the hydrophobicity of unwanted (gangue) minerals, so that these minerals report to the slurry and are discarded as tail. The main alternative technique in froth flotation is xe2x80x9creverse flotationxe2x80x9d. This consists of floating the gangue minerals as a concentrate and keeping the mineral of interest on the slurry.
Chemicals that promote hydrophobicity of a mineral are called out that mineral""s xe2x80x9cpromoterxe2x80x9d or xe2x80x9ccollector.xe2x80x9d Collectors based on fatty acids have long been used in collecting one or more of the oxide minerals such as fluorspar, iron ore, chromite, scheelite, CaCO2, MgCO2, apatite, or ilmenite.
Also, early work used alkali metal salts of fatty acids, or soaps derived from natural oils by the process known as saponification. When an oil containing triglycerides is treated with a caustic solution under certain harsh processing conditions, the triglycerides disassociate into the alkali metal salts of the component fatty acids. The dissociation of the triglycerides into neutralized fatty acids is the saponification process. These neutralized fatty acids are soaps that act as non-selective flotation collectors.
Compounds containing sulfur, such as xanthanes, thionocarbamates, dithiophosphates, and mercaptans, will selectively collect one or more sulfide minerals such as chalcocite, chalcopyrite, galena, or sphalerite. Unfortunately, sulfur based collectors are often toxic, have repugnant odors or both. Amine compounds are used to float KCl from NaCl and for silica flotation. Petroleum-based oily compounds such as diesel fuels, decant oils, and light cycle oils, are often used to float molybdenite. Those oils are also used as an xe2x80x9cextruderoilxe2x80x9d that reduces the dosage of other more expensive collectors in the amine flotation of KCl.
Previous work on sulfide minerals has indicated that molecules containing sulfur are useful compounds for the froth flotation of sulfide minerals. These collectors are usually grouped into two categories: water-soluble and oil (i.e., hydrophobic) collectors. Water-soluble collectors such as xanthates, sodium salts of dithiophosphates, and mercapto benzothiazole have good solubility in water (at least 50 gram per liter) and very little solubility in alkanes. Oily collectors, such as zinc salts of dithiophosphates, thionocarbamates, mercaptans, and ethyl octylsulfide, have negligible solubility in water and generally good solubility in alkane.
Currently used collectors for most sulfide minerals are sulfur-based chemicals such as xanthanes, thionocarbamates, dithiophosphates, or mercaptans. These chemicals have problems with toxicity and or repugnant odors. In addition, these collectors can be very expensive. Therefore, a need exists for new collectors that are effective but not toxic or odiferous.
This invention is directed to a method of beneficiating a mineral sulfide-containing material or a metallic species of gold, silver, copper, palladium, platinum, iridium, osmium, rhodium, or ruthenium by froth flotation in the presence of a collector as well as a collector for beneficiation of sulfide minerals, precipitates, or metallic species. In both aspects, the collector includes at least one oil which is either an essential oil or a natural or synthesized oil comprising triglycerides containing fatty acids of only 20 carbons or less, or an ester made from a fatty acid and an alcohol.
In the method aspect of the invention, the method includes the steps of (1) providing an aqueous slurry of the mineral sulfide-containing or metal-containing material, (2) adding a selective collector to the slurry, the collector comprising at least one oil selected from the group consisting of (a) a natural oil or synthesized oil comprising triglycerides containing fatty acids of only 20 carbons or less, or an ester made of fatty acid and an alcohol; and (b) an essential oil; (3) selectively floating the mineral sulfide; and, then (4) recovering the mineral.
In the collector aspect of the invention, a collector is provided for beneficiation of sulfide minerals or precipitates from ores, concentrates, residues, tailings, slags, or wastes. The collector includes at least one sulfur-containing sulfide mineral flotation promoter; and at least one oil selected from the group consisting of (1) a natural or synthesized oil comprising at least one triglyceride, or at least one ester made from a fatty acid and an alcohol; and (2) an essential oil.
This invention has an advantage that the specified triglyceride, specially, or essential oil will selectively float sulfide minerals by itself or mixed with other collectors. This and other advantages will be apparent from the detailed description of the invention that follows.
The subject invention provides materials and methods useful in the recovery of minerals. These materials and methods are specifically applicable to froth flotation procedures; whereby, minerals are removed and recovered from complex mixtures of ores, residues, concentrates, slags, and wastes. The subject invention can be used in remediation processes to remove unwanted materials or may be used in mining processes to recover valuable minerals. Specifically exemplified herein is the use of certain triglycerides, esters of the fatty acids and long chain alcohols, and essential oils of both terpene and aromatic chemistries. Any of these oils may be used alone, in mixtures, or in combination with other collectors.
In the method aspect of the invention, the method includes the steps of (1) providing an aqueous slurry of the mineral sulfide-containing or metal-containing material, (2) adding a selective collector to the slurry, the collector comprising at least one oil selected from the group consisting of (a) a natural oil or synthesized oil comprising triglycerides containing fatty acids of only 20 carbons or less, or an ester made from a fatty acid and an alcohol; and (b) an essential oil; (3) selectively floating the mineral sulfide; and, then (4) recovering the mineral.
In the collector aspect of the invention, a collector is provided for beneficiation of sulfide materials or precipitates from ores, concentrates, residues, tailings, slags, or wastes. The collector includes at least one sulfur-containing sulfide mineral flotation promoter; and at least one oil selected from the group consisting of (1) a natural or synthesized oil comprising at least one triglyceride, or at least one ester made from a fatty acid and an alcohol; and (2) an essential oil.
Preferably the mineral sulfide-containing material selected from the group consisting of chaiconine, chalcopyrine, bornite, galena, sphalerite, pentlandite, molybdenite, and other sulfide minerals containing silver, gold, platinum, palladium, iridium, rhodium, and osmium, either in the crystal structure or in association as an independent mineral species, and combinations thereof. This material may be derived from ores, concentrates, precipitates, residues, tailings, slag, or wastes.
Alternatively, the method may be used for acting upon metallic species such as gold, silver, copper, palladium, platinum, iridium, osmium, rhodium, and ruthenium by froth flotation in the presence of a collector. The metallic species may be from material derived from any ore, concentrate, residue, tailings, slag, or waste.
The oils used according to the subject invention can be readily obtained and used by a person trained in the teaching of this patent. The natural oils identified in this invention are obtained directly or indirectly from plants or animals.
In a specific embodiment, the process of the subject invention can comprise the following steps:
a) pulverizing a mineral-containing material to appropriate fine-sized particles;
b) mixing the pulverized particles with water to produce a slurry;
c) agitating the mixture and adjusting its pH as necessary to produce a conditioned slurry;
d) adding a sufficient amount of a naturally occurring oil or a mixture thereof to the slurry with conditioning to render the surfaces of the particles containing the desired minerals hydrophobic;
e) agitating the resultant slurry under conditions and for a time sufficient to obtain a sufficiently homogenous mixture;
f) adding a frothing agent to the homogenous mixture in an amount sufficient to cause frothing of the homogenous mixture upon injecting air or other gases;
g) injecting air or other gas into the mixture to form bubbles in the resultant composition in an amount and under conditions sufficient to cause the hydrophobic particles to become attached to the bubbles and cause the resultant bubbles with attached particles to rise and form forth; and
h) separating the froth fraction and recovering the desired mineral.
In a specific embodiment of the subject invention, the mixture produced in Part (b) will have between about 1% to 75% solids by weight. In Part (c) of the process, the pH may be adjusted to anywhere in the 5 to about 13 pH range, with particularly good results in the 7 to 10 pH range. With regard to Part (d), a natural oil, such as cottonseed, may be used as the only collector or it may be used with other collector compounds. In a preferred embodiment, the concentration of the natural oil used according to the subject invention can range from about 1 gram per ton of ore to about 1,000 grams per ton of ore. The temperature range of the use of these compounds goes from 5 to 75 degrees Centigrade with most normal operations in the 15 to 40 degree Centigrade range. Preferably, the flotation conditions should be kept mild enough to prevent significant disassociation of the triglycerides, or other components, contained in the natural oils into fatty acids, and to prevent the subsequent saponification into fatty acid soaps. The selectivity of the flotation when using oils according to this invention is evidenced by the selective recovery of the minerals, and substantiates this observation. A skilled artisan trained in the teachings of this patent can adjust the concentration and conditions to achieve optimization of the process for a particular mineral once a collector compound has been identified as useful for that mineral species.
Gold, silver and platinum metal group metals (platinum, palladium, rhodium, and iridium) are often associated with sulfide minerals. These metals may be also effectively collected by the oils described in this patent either alone or in combination with another collector.
The invention is specifically exemplified for the recovery of certain sulfide minerals. A skilled artisan, having the benefit of the instant disclosure, could readily adapt the process for the recovery and/or removal of a broad range of sulfide minerals, silver, gold or platinum group metals.
It was found, however, that there are unexpected benefits of using certain organic compounds containing no sulfur, no nitrogen and no phosphorous for selective froth flotation of certain sulfides. These molecules contain oxygen in a variety of functional groups such as triglycerides and esters. These groupings occur in many natural oils, such as cottonseed, corn, palm, safflower, jojoba, and clove. Surprisingly, many of these oils are non-toxic and are used in foodstuffs throughout the world. The oils run in price from $0.40 per kilogram to over $125 per kilogram.
It was also unexpected that blends of these oils with each other and with standard collectors frequently exhibit synergistic or enhanced effects, in that a mixture of a sulfur containing collector with a non-sulfur containing collector may perform better than either of the components alone, and mixtures of multiple components may perform better than a two-component blend. This invention is uniquely suited to such mineral species as chalcocite, chalcopyrite, bornite, galena, and sphalerite. However, sulfur species such as pyrite are not as readily floated by these non-sulfur-containing collectors.
Most natural plant and animal oils are triglycerides of mixtures of fatty acids. A triglyceride is simply the reaction product of a carboxylic acid and glycerol. The general formula for a triglyceride is shown in FIG. 1. Triglycerides are generally made from fatty acids with typically 10 to 24 carbon atoms and from 0 to 3 double bonds in their chains. Some triglycerides are made from hydroxyl fatty acids that have an alcohol group somewhere in the chain. An example of this is castor oil. Another oil, oiticicia, has three double bonds and a ketone functionality in its composition. 
Saturated or highly saturated oils, such as coconut oil, contain triglycerides made from a zero to a low percentage of fatty acids having double bonds. Linseed oil contains a high percentage of linolenic acid oil, an 18 carbon fatty acid with three double bonds (expressed as C18:3). The composition of some common natural oils is shown in Table 1. The iodine value is a measure of the unsaturation of the oil. The saturated fat column is for the percentage of saturated fat when the extract chain length is unspecified. A given type of oil composition will vary with the variety of plant, the growing conditions and the treatment of the oil after pressing. For instance, there are both high and low erucic acid (C22:1) species of canola oil. Some canola oil is also hydrogenated (hydrogen reacted with the double bonds) before being sold.
It was unexpectedly found, however, that oils containing triglycerides that have fatty acids with 20 carbon atoms or less, perform much better than oils, such as canola oil, that contain triglycerides with fatty acids having 22 carbons or more, such as erucic acid (C22:1). Moreover, since oils containing triglycerides of fatty acids with twenty carbon atoms or less do not contain free fatty acids, they do not behave as either fatty acids or soaps of fatty acids. The selective nature of these oils in flotation was surprising because fatty acids and fatty acid salts (i.e., soaps) are very non-selective.
Other sources of triglycerides are animal oils. Commercially available animal oils have a limited range of unsaturation values. A highly unsaturated lard oil will have triglycerides containing 46% C1xc3x971(oleic acid). 15% C1xc3x972(linoleic acid). 1% C1xc3x972(linolenic acid), and 62% saturated fatty acids.
There are some unique natural oils. Sperm whale oil contains esters made from long chain fatty acids and long chain fatty alcohols instead of esters of the fatty acid and glycerol as in triglycerides. Both the fatty acid and long chain alcohol usually contain at least 1 double bond. Sperm whale oil is, of course, no longer available due to whaling restrictions. However, its replacements, jojoba oil (vegetable) and orange roughy oil (fish), have the same basic chemistry as sperm whale oil. The only differences between them are in the carbon numbers (chain length) of the various components of the oils.
Chemical manufacturers can synthesize a long chain ester from a fatty acid and a long chain alcohol. One example of a xe2x80x9csynthesized oilxe2x80x9d or xe2x80x9csynthetic oilxe2x80x9d is 2-butyloctyl oleic acid ester. This compound contains one unsaturated site in the fatty acid molecule. The carbon numbers of the largest fractions of these oils are shown in Table 2.
Preferably, the natural oils used in this invention include triglycerides that contain only fatty acids having a carbon number less than 20. Also, it is preferred that the triglycerides include an alcohol, an ether, an aldehyde, or a ketone functional group, or an aromatic group. A preferred group of natural oils includes cottonseed, corn, linseed, rice bran, safflower, soybean, avocado, jojoba, menhaden, lard, castor, cod liver, tung, oiticicia, apricot, sunflower pistachio, herring, and coconut oils. A more preferred group of natural oils includes cottonseed, corn, linseed, rice bran, safflower, soybean, avocado, jojoba, menhaden, lard, castor, cod liver, tung, and oiticicia. A still more preferred group of natural oils includes cottonseed, corn, linseed, rice bran, safflower, soybean, avocado, jojoba, menhaden, lard, and castor oils. An even more preferred group of natural oils includes cottonseed, corn, linseed, rice bran, safflower and soybean. The most preferred natural oil is cottonseed oil.
Another class of naturally occurring oils is called xe2x80x9cessential oilsxe2x80x9d or xe2x80x9cvolatile oils.xe2x80x9d These are fragrant oils derived from various plant species. Since ancient Egyptian times, they have been used for their fragrance and reputed medicinal properties. The chemistry of most of these compounds is based on either terpene chemistry or aromatic chemistry.
Terpenes are defined as compounds that can be assembled from two or more molecules of isoprene (C5H8) and the alcohol, aldehyde, and ketone derivatives of such compounds. A terpene compound can be defined as a monoterpene, sesquiterpene, or diterpene compound based on whether it contains 2, 3, or 4 isoprene units, respectively. Within each of these classifications the compounds can be further defined as being acyclic, monocyclic, bicyclic or tricyclic depending on whether the terpene contains, respectively, 0, 1, 2, or 3 ring structures (only diterpenes are tricyclic). Tricyclic diterpenes are generally solids.
Aromatic chemistry for essential oils refers to the chemistry of derivatives of benzene. The two most common aromatic components of essential oils are cinnamaldehyde and eugenol. These are obtained from cinnamon and clove oil. Their structures are shown in FIG. 2. 
Most essential oils have one single major terpene or aromatic component or are a mixture of closely related terpenes or aromatics. Table 3 shows the composition of some representative essential oils. Note that any particular oil""s composition can vary with variety, weather, etc.
Preferably, the essential oils used in the methods of this invention include either a terpene compound or an aromatic compound. More preferably, the essential oil includes a terpene derivative having a functional group selected from an alcohol, an ether, an aldehyde, and a ketone. Specific preferred essential oils include limonene, citronella, eugenol, eucalyptus globus, camphor, and clove oil. A more preferred group of essential oils includes limonene and citronella.
As work with the triglycerides, esters and alcohols have indicated, other oxygen-containing compounds such as aldehydes, ketones, and ethers of sufficient carbon number to be water-insoluble function as collectors for sulfide minerals. These compounds may or may not have carbon-carbon double bond(s).
The literature has shown that emulsified collectors can give better results than unemulsified collectors. Emulsification should also allow the combining of inexpensive water-soluble xanthates and sodium sulfide into the oils. Other water-soluble collectors that may be amenable to emulsification into oil include sodium dithiophosphates and mercapthobenzothiazole.
The invention also includes the use of the plant and animal oil collectors blended with known commercial collectors. Commercial collectors are also known as xe2x80x9cflotation promotersxe2x80x9d and are identified herein as xe2x80x9csulfur-containing flotation promoters.xe2x80x9d These common commercial promoters are usually separated into two classes of chemicals based on their water solubility. Water soluble sulfur containing collectors, or promoters, used in the froth flotation of sulfide minerals include such well-known collectors as xanthates and dithiophosphates. These are usually used as sodium or potassium salts of the respective organic acids. An example of a water-soluble collector would be sodium isopropyl xanthate. The other class of sulfur containing collectors would be water insoluble collectors. These collectors are generally referred to as oil collectors, because they are liquids that are insoluble in water. These collectors include thionocarbamates, mercaptans, organic sulfides, and the zinc salts of dithiophosphates. Even though these compounds are chemical reaction products, they are called oils.
Another grouping of collectors commonly used in froth flotation of substances such as coat, sulfur, and molybdenite are petroleum-based products that are truly oils. These oils generally consist of kerosene, vapor, diesel, fuel, turbine, light cycle, and carbon black oil. These petroleum oils are generally called xe2x80x9cextender oilsxe2x80x9d are generally exhibit poor collecting ability and very poor selectivity when used by themselves. To distinguish these xe2x80x9cpetroleum-based collectorsxe2x80x9d from other described collectors, the term xe2x80x9coil collectorxe2x80x9d used in this text means a synthesized organic chemical compound containing sulfur such as the group of xe2x80x9csulfur-containing flotation promotersxe2x80x9d described above.
This invention also includes the use of any of these aforementioned natural, synthetic or essential oils in combination. The essential oils are found to be very potent collectors. As such they are ideally suited for use in small amounts in combination with other oils or with other sulfide-containing flotation promoters. Good results have been obtained when using the essential oils in amounts of less than 10% weight blended with other collectors. Preferably, less than 2% by weight is used.
Also, any of the natural oils including the higher carbon fatty acid-containing triglycerides, and in particular, the preferred natural oils alone or in combination with other preferred oils, may be used blended with any number of sulfur-containing flotation promoters. In such blends, the natural oils make up preferably between 20% and 80% by weight of the blend, and the flotation promoters make up preferably between the remaining 80% and 20% by weight of the blend. Optionally, a frother may be added to that blend, preferably in an amount between about 10% and 40% by weight of the composition. Frothers are commercially available compositions that are used to develop a froth or foam on top of a slurry that has been aerated. A particular suitable frother is one such as that sold by NALCO under the designation 9743. Methyl isobutyl carbonol (MIBC), also known as methyl amyl alcohol, is one of the most widely used frothers in the mining industry.
The collectors and blends of collectors in accordance with the methods of this invention can be used in standard froth flotation processes known by those skilled in the art and modified by the teachings of this patent as illustrated in the following examples.